ATM: Most ATM’s here will charge a fee to withdraw, highest I’ve seen is S/18. However, Banco de la Nacion/Multi-Red do not charge a fee but limited to S/400 (approx £90) per day. BCP also do not charge, but limited to 1 withdrawal of S/700 max per month.
POS: Chip, Swipe and Contactless all work here. Some machines will take the money in local currency, others will prompt (obv choose local currency for MC rate). Also, in Peru they have a system where you can choose to pay over 12 months. I have no idea if it would actually work (I doubt it) but you need to choose “sin quotas”.
Acceptance: All big retailers, chains etc accept Mastercard. Medium businesses are probably 60/40 in MC favour, but Visa is more common. Small restaurants etc are cash only usually. Outside of the cities (i.e. Lima) you’ll definitely need cash for most things.
Notes: Credit cards in Peru require ID to be presented, however debit cards do not. However retailers may still ask and it’s at their discretion. Usually when they’ve asked its because they have assumed it’s a credit card.